Transmit power control methods in radio communication systems using a CDMA system or the like have been known in which transmit power at a transmitter is controlled so as to make received power at a receiver constant even when fluctuations in the propagation path occur.
As a first transmit power control method, a closed loop transmit power control method is known in which a receiver compares a measured desired wave to interference wave power ratio (SIR) to a desired SIR, and sets transmit power control bits based on a result of the comparison.
As a second transmit power control method, an outer loop transmit power control method is known in which a receiver compares a measured receive error rate of a received signal to a preset target receive error rate, corrects a target SIR based on a result of the comparison, and sets transmit power control bits based on the corrected target SIR.
As a third transmit power control method, a closed loop transmit power control method is known in which a receiver selects a data piece which requires the highest data quality from among the data pieces included in a received signal, and controls target circuit quality (target SIR) so that the data quality of the selected data piece is satisfied. By using this closed loop transmit power control method, even when a plurality of data pieces requiring different data qualities are multiplexed on the same channel, transmit power control can be properly performed.
With reference to FIG. 1, a radio communication system for implementing the above-described third transmit power control method will be described. For a radio control station shown in FIG. 1, a radio control station 3 is provided with main functions of outer loop transmit power control, and a base station 2 is provided with main functions of closed loop transmit power control.
As shown in FIG. 1, the base station 2 is configured with an amplifier unit 21, a demodulator unit 25, a modulator unit 22, a frame generating unit 23, a pattern determining unit 24, and a SIR measuring unit 26.
The amplifier unit 21 is configured to amplify a signal received from a mobile station 1 for output. The amplifier unit 21 is also configured to amplify a spread signal outputted from the modulator unit 22 to a certain output for transmission to the mobile station 1.
The modulator unit 22 is configured to perform data modulation processing and spread modulation processing on a transmission frame outputted from the frame generating unit 23 for output to the amplifier unit 21.
The frame generating unit 23 is configured to add transmit power control bits determined by the pattern determining unit 24 to data bits to be transmitted, thereby forming a transmission frame.
The pattern determining unit 24 is configured to determine a transmit power control bit pattern, based on a SIR measured by the SIR measuring unit 26 and a stored target SIR. Here, a target SIR stored is periodically communicated from the radio control station 3.
The demodulator unit 25 is configured to perform despread demodulation processing and data demodulation processing on a signal outputted from the amplifier unit 21 for output to the SIR measuring unit 26 and the radio control station 3. The SIR measuring unit 26 is configured to measure a SIR based on a signal outputted from the demodulator unit 25.
The radio control station 3 is configured with a transport channel (TrCH) separating unit 31, channel (CH) quality measuring units 321 to 32n, transport channel target SIR updating units 331 to 33n, and a target SIR determining unit 34.
The transport channel separating unit 31 is configured to separate a plurality of transport channels from a signal outputted from the demodulator unit 25 of the base station 2.
The channel quality measuring units 321 to 32n are configured to measure the channel qualities of the separated transport channels.
The transport channel target SIR updating units 331 to 33n are configured to compare channel qualities measured by the channel quality measuring units 321 to 32n with preset target channel qualities for respective transport channels, and to update target SIRs for the respective transport channels.
Also, the transport channel target SIR updating units 331 to 33n are configured to update the target SIRs for the respective transport channels, based on the target SIR communicated from the target SIR determining unit 34.
The target SIR determining unit 34 is configured to compare the updated target SIRs for the respective transport channels, and to determine a target SIR which satisfies the channel qualities of all transport channels for communication to the base station 2.
At the same time, the target SIR determining unit 34 is configured to communicate the determined target SIR to the respective transport channel target SIR updating units 331 to 33n. 
In some cases, in the conventional radio communication system shown in FIG. 1, the radio control station 3 communicates the determined target SIR to the base station 2 in predetermined periods, not in real time, for the purposes of reducing the load of the radio control station 3 and reducing the circuit capacity between the radio control station 3 and the base station 2.
The conventional radio communication system, however, has the problem that when user transport channels and a control transport channel are multiplexed into a signal, even if a receive error occurs in the control transport channel, for example, a target SIR is not improved until a predetermined period comes, and there is the possibility that a long predetermined period can prevent flow of control data and establishment of communication.
The present invention has been made in view of the above problems, and has an object of providing a controller equipment and a radio communication method with which, in the case where a radio control station communicates a target SIR in outer loop transmit power control to a base station in predetermined periods, not in real time, an adequate circuit quality can be maintained with a minimum increase in the load of the radio control station and a minimum increase in the circuit capacity between the radio control station and the base station.